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Complex Intermediate (complex + intermediate)
Selected AbstractsSubstituent effect and multisite protonation in the fragmentation of alkyl benzoatesJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 3 2002Chagit Denekamp Abstract The dissociation of protonated alkyl benzoates (para H, CN, OMe and NO2) into protonated benzoic acids and alkyl cations was studied in the gas phase. It was found that the product ratio depends on the substituent at the para position of the phenyl ring. The substituent effect is probably the result of the formation of an ion,neutral complex intermediate that decomposes to an ion and a neutral, according to the relative proton affinities of the two moieties. The experimental results and theoretical calculations indicate that the favored protonation site in these compounds is the ester's carbonyl and that proton transfer from the phenyl ring to the ester group is very likely to occur under chemical ionization conditions. It is most probable that the carbonyl protonated form is a common intermediate in the fragmentation process, regardless of the protonation site. Copyright © 2002 John Wiley & Sons, Ltd. [source] Investigation of the Decomposition Mechanism and Thermal Stability of Nitrocellulose/Nitroglycerine Based Propellants by Electron Spin ResonancePROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 2 2007Anton Chin Abstract Nitrocellulose based (NC) and nitroglycerin based (NG) propellants often have a fixed acid and water content during the manufacturing time. After manufacture, the quantity and ratio of acid/water will continue to vary depending upon the conditions of storage and operation. The level of variation depends on many factors such as loading density, temperature, volume of ullage and sealing condition of the containing cartridge, just to name a few. As described in this paper and other literature, the degradation mechanisms and aging processes of NC/NG based propellants are extremely complicated. This paper describes the details of the application of Electron Spin Resonance (ESR) to study if the free-radical mechanism is involved in the decomposition of nitrocellulose and nitroglycerin. Due to the high free-radical intensity possessed by the propellant composition, we believe that a , complex intermediate may be formed between DPA and NG and/or NC. The formation of a , complex intermediate is not preferred because it may enhance the rate of decomposition of nitrate esters. [source] Theoretical Study on the Mechanism of the Cycloaddition Reaction between Methylidenesilene and EthyleneCHINESE JOURNAL OF CHEMISTRY, Issue 3 2006Xiu-Hui Lu Abstract The mechanism of a cycloaddition reaction between singlet methylidenesilene and ethylene has been investigated with MP2/6-31G, and B3LYP/6-31G, methods, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. Energies of the involved conformers were calculated by CCSD(T)//MP2/6-31G, and CCSD(T)//B3LYP/6-31G, methods, respectively. The results show that the dominant reaction pathway of the cycloaddition reaction is that a complex intermediate is firstly formed between the two reactants through a barrier-free exothermic reaction of 13.3 kJ/mol, and the complex is then isomerized to a four-membered ring product P2.1 via a transition state TS2.1 with a barrier of 32.0 kJ/mol. [source] Transition metal catalyzed carbon-silicon bond forming reactions using chlorosilanes promoted by Grignard reagentsTHE CHEMICAL RECORD, Issue 1 2007Jun Terao Abstract New catalytic CSi bond-forming reactions using chlorosilanes are described. These reactions proceed efficiently under mild conditions by the combined use of Grignard reagents and transition metal catalysts, such as Ti, Zr, Ni, and Pd. It is proposed that ate complex intermediates formed by the reaction of transition metals with Grignard reagents play important roles as the active catalytic species. The present study demonstrates the practical use of chlorosilanes in transition metal catalyzed silylation reactions providing convenient methods for allyl- or vinylsilane synthesis. The reaction pathways of these transformations as well as the scope and limitations are discussed. © 2007 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 7: 57,67; 2007: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20101 [source] | ||||||||||